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When all a society has to build with is stone and wood, the individual span lengths of a simple beam bridge are very short. New technology was needed to: Span greater distances Withstand greater loads Withstand the effects of weathering SOLUTION: THE ARCH Bridges

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The need to span increased distances continued to pressure bridge designers. With the new material of steel available, with its superior performance in tension, new designs made bridges longer and stronger. Steel made the TRUSS BRIDGE possible. Bridges

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Still, longer spans were required. As technology developed, and materials became available, a new variation on an old design was possible. This dramatically increased the total span length. This is the SUSPENSION BRIDGE

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The January 17, 1995 Kobe earthquake had its epicenter right between the two towers of the Akashi Straits Bridge. The original planned length was 1990 meters for the main span, but the seismic event moved the towers apart by almost a meter. Since construction of the deck had not yet begun, the change was easily accommodated in the slightly altered final design. The towers of the bridge contain tuned mass dampers in order to diminish the vibrations in the structure during earthquakes.

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The most recent development in bridge design does not make any dramatic increases in span length. Rather, it allows mid-sized bridges to built with less material, therefore making bridges more economical to build and maintain. These are the CABLE - STAYED bridges Bridges

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What does the immediate future hold? As new strong, lightweight synthetic materials become more common, ever more impressive bridges will be built. The current “next step” is to bridge the Straits of Gibraltar. Bridges